1. Field of the Invention
The present invention relates to a bump for a semiconductor package, a semiconductor package applying the bump, and a method for fabricating the semiconductor package.
2. Description of the Background Art
In general, a semiconductor package fabricated by wire boding is larger in size than a semiconductor chip because electrode terminals of a printed circuit board (PCB) and electrode pads of the semiconductor chip are electrically connected by a conductive wire. In addition, wire bonding requires a long time, which is disadvantageous in a slim and lightweight shape and a mass production.
According to high integration, high performance and high speed tendencies of the semiconductor chip, there have been various attempts for a slim and lightweight shape and mass production of the semiconductor package. For example, there has been suggested a semiconductor package in which electrode pads of a semiconductor chip are electrically to electrode terminals of a PCB through solder or metal bumps formed on the electrode pads of the semiconductor chip.
Normally, a flip chip ball grid array method is applied to the semiconductor package using the solder bumps, and a chip-on-glass method is applied to the semiconductor package using the metal bumps.
The flip chip ball grid array method fabricates a semiconductor package by electrically connecting solder bumps contacting electrode pads of a semiconductor chip to pads of a substrate, underfilling the solder bumps to be protected from external environment or mechanical problems, and adhering solder balls to the rear surface of the substrate which the semiconductor chip contacts to be electrically connected to electrode terminals of a PCB.
The chip-on-glass method fabricates a semiconductor package by electrically connecting electrode pads of a semiconductor chip to electrode terminals of a PCB through metal bumps contacting the electrode pads of the semiconductor chip, by thermocompression bonding and hardening the metal bumps to the electrode terminals of the PCB by the medium of a polymer containing anisotropic conductive particles.
FIG. 1 is an exemplary diagram illustrating the semiconductor package using the metal bump. Referring to FIG. 1, the semiconductor package includes a semiconductor chip 20 on which an electrode pad 10 has been formed, a protecting film 30 formed on the surface of the semiconductor chip 20, for selectively exposing the electrode pad 10, a metal adhering layer 40 formed on the electrode pad 10, and extended from the upper portion of the electrode pad 10 to the upper portion of the protecting film 30 around the electrode pad 10, a metal bump 50 formed on the metal adhering layer 40, and a PCB 70 on which an electrode terminal 60 contacting the top surface of the metal bump 50 has been formed.
As described above, in the semiconductor package fabricated according to the chip-on-glass method, the metal bump 50 is formed to contact the electrode pad 10 of the semiconductor chip 20, and thermocompression bonded and hardened to the electrode terminal 60 of the PCB 70 by the medium of a polymer (not shown) containing anisotropic conductive particles, thereby electrically connecting the electrode pad 10 of the semiconductor chip 20 to the electrode terminal 60 of the PCB 70. As compared with the general semiconductor package fabricated by wire bonding, a transmission distance of electric signals is reduced to obtain a high speed, and a size of the semiconductor package is reduced, which is advantageous in a slim and lightweight shape.
On the other hand, a semiconductor process can be applied to the semiconductor chip 20. It is thus possible to minimize a pitch between the electrode pads 10 and a pitch between the bumps 50. Conversely, the semiconductor process cannot be applied to the PCB 70. It is this difficult to reduce a size of lines and electrode terminals 60.
When the pitch between the electrode pads 10 of the semiconductor chip 20 and the pitch between the bumps 50 are minimized, the pitch between the bumps 50 does not correspond to the pitch between the electrode terminals 60 of the PCB 70, to cause contact failure. Accordingly, the bump 50 contacts the patterned lines adjacent to the electrode terminals 60 of the PCB 70.
Still referring to FIG. 1, the metal adhering layer 40 is formed on the electrode pad 10 of the semiconductor chip 20 selectively exposed by the protecting film 30, and the metal bump 50 is formed by plating. In this case, in order to prevent the electrode pad 10 of the semiconductor chip 20 from being damaged in an etching process of the metal adhering layer 40, the metal adhering layer 40 is extended from the upper portion of the electrode pad 10 to the upper portion of the protecting film 30 around the electrode pad 10. The metal bump 50 is formed on the metal adhering layer 40. The center of the top surface of the metal bump 50 is more caved than the edges thereof.
In the case that the metal bump 50 is thermocompression bonded and hardened to the electrode terminal 60 of the PCB 70 by the medium of the polymer containing anisotropic conductive particles, an electric contact resistance between the metal bump 50 and the electrode terminal 60 of the PCB 70 is increased, and an adhesion property thereof is deteriorated.
FIG. 2 is an exemplary diagram illustrating the bump 50 and the electrode terminal 60 of the PCB 70 coupled through a solder cap formed on the top surface of the bump 50 in FIG. 1.
As illustrated in FIG. 2, the metal bump 50 contacts the electrode terminal 60 of the PCB 70 through the solder cap 80 formed on its top surface.
The solder cap 80 formed on the top surface of the bump 50 generates alpha particles by radiation during the process for fabricating the semiconductor package, thereby causing mis-operation of the semiconductor chip 20. Here, the bump 50 is formed with a set height H by a photosensitive photoresist, and thus the solder cap 80 is separated from the semiconductor chip 20 by the set height H, to prevent mis-operation of the semiconductor chip 20 by alpha particles.
The sidewalls of the bump 50 formed by the photosensitive photoresist are not vertical but inclined at a predetermined angle. In order to form the bump 50 with the preset height H, it is necessary to obtain a sufficient area of bump 50 contacting the electrode pad 10 of the semiconductor chip 20. When the pitch between the electrode pads 10 of the semiconductor chip 20 and the pitch between the bumps 50 are reduced, shorts occur between the bumps 50.
In addition, when the solder cap 80 contacts the electrode terminal 60 of the PCB 70, the solder cap 80 is pressed flat. Accordingly, if the pitch between the electrode pads 10 of the semiconductor chip 20 and the pitch between the bumps 50 are reduced, shorts occur between the bumps 50.
As a result, the conventional semiconductor package is disadvantageous in a slim and lightweight shape with multi-pin of the semiconductor chip 20.